The broad long-term objective of the proposed research is to determine the role of the retinoid signal transduction pathways in olfactory neuroepithelium. The hypothesis is that retinoic acid plays an important role in modulating cellular homeostasis and differentiation in the olfactory epithelium of adult animals. The specific aims are: (I)To identify retinoic acid receptors expressed in olfactory mucosa. The retinoic acid receptor (RAR and RXR) isotypes and isoforms in the olfactory tissue of adult mice will be detected by RNAPCR analysis of total RNA. The expression of RAR and RXR proteins will be detected by immunoblot analysis of nuclear extracts from rat olfactory mucosa with isotype-specific antibodies, and the presence of functional RARs and RXRs will be determined by gel mobility shift assays with oligonucleotides containing consensus binding site for different families of retinoic acid receptors. The cellular localization of identified RARs and RXRs will be examined by immunohistochemical studies. The presence of functional retinoic acid receptors would indicate that olfactory epithelial cells of adult animals are capable of responding to retinoids. (2)To examine the effects of dietary Vitamin A deficiency on the olfactory expression of RARbeta and the regeneration of the olfactory epithelium following chemically induced degeneration. Adult rats will be fed a control diet or a vitamin A- deficient diet, or diets supplemented with retinoic acid. The olfactory expression of RARbeta, a known target gene for retinoic acid, will be examined by immunoblot and RNA blot analysis. Olfactory degeneration will be induced by exposure to methyl bromide. The degeneration and subsequent regeneration of the olfactory epithelium will be monitored by the levels of olfactory marker protein and olfactory-specific P450 2G1. A delay or failure to regenerate in the vitamin A-deficient animals would strongly support the hypothesis that retinoids play an important role in the cellular differentiation and neurogenesis in the olfactory mucosa of adult animals. The results will improve our understanding of the molecular basis of olfactory sensory disorders such as anosmia.